Many communication networks employed today, such as Ethernet Systems and other local area networks (or LAN's), consist of a series of field devices such as monitors, access terminals and other peripherals, which receive and transmit a variety of communication signals. In fieldbus systems, peripheral devices communicate with one or more main signal sources via a fieldbus line. Fieldbuses are a special type of LAN which can allow communication with a variety of sensors and activators or other peripherals. Each peripheral device is connected to this fieldbus line at various termination points. A general overview of one type of these systems is provided in FIG. 1. In general a fieldbus is used to monitor or control one or more pieces of production equipment.
Information is typically transmitted along the fieldbus in synchronized frames, which contain identifying information for the particular device sending the signal, such as the nature and length of the frame, and possibly a data or message segment. If the network is not operating properly, errors may be introduced into individual signal frames, or a group of related signal frames, which may cause damage to devices on the network or the loss of critical information. Errors may be introduced in a variety of ways. For example, noise may be introduced into the communication signal due to surrounding microwave or radio transmissions. Additionally, a mismatch in impedance between the termination point for particular devices and the fieldbus line may cause severe attenuation and delay in the transmission of the communication signal, causing an interference between two or more transmitted signals, or loss of the signal altogether. If a malfunction occurs in a signaling device, errors are introduced into individual frames or groups of related frames, which may cause the data to be received and stored incorrectly or not received at all. These signal errors may cause severe damage to or misoperation of equipment which is operated by the network, or the loss of crucial information. In addition, considerable time and effort may be expended in attempting to locate the cause of the error.
Previously, various inadequate system analyzers have been introduced to monitor fieldbus communication networks to detect communication errors. In these prior art systems, one or more message signals transmitted on the network are first stored electronically and then analyzed at a future time. This creates the severe disadvantage that errors may remain undetected for long periods of time, increasing both the actual or potential damage to, or misoperation of, the equipment operated by the network due to the faulty signal and, consequently, the cost of repair or replacement of damaged devices. Additionally, important transmitted data may be irretrievably lost due to the delay in detecting the malfunction. This creates the extreme disadvantage in the prior art that the communication network is not monitored accurately or efficiently, leading to increased cost of repair and increased potential damage or misoperation, since these prior art systems are not capable of detecting or displaying signal errors in real time.
Additionally, in previous fieldbus system analyzers, it has not been possible to monitor a communication signal while simultaneously generating a coordinated simulated signal from the analyzer with which to elicit a specific system response and make a real-time comparison in order to detect signal errors. In prior art systems, a simulated signal is produced separately and cannot be coordinated with a recorded communications signal. This creates a great delay in the detection and analyzation of communication errors and greatly increases the potential damage to or misoperation of the equipment operated by the communication network.
Because of the tremendous cost of modern manufacturing and the potential environmental and safety hazards that its misoperation may entail, a method and apparatus for monitoring and analyzing a communication network is needed which accurately and efficiently monitors the network, and quickly detects signaling errors. Additionally, a monitoring and detecting system is needed which combines a network analyzer with a simulator to more quickly and accurately detect signaling errors and thereby greatly reduce the cost of repair or replacement of network components and the cost and side effects of network misoperation.